Satellite communication requires precise antenna positioning. When attempting geosynchronous satellite communication from a stationary or nearly stationary location, a satellite antenna, once properly positioned, may require little or no adjustment. When adjustments are required, they are predictable and easily accomplished.
However, when attempting satellite communication on the move, the satellite antenna must be constantly and precisely adjusted and repositioned. For example, a satellite antenna affixed to a vehicle must be able to point the beam to within less than 0.5° of a desired orientation while the vehicle is moving; vehicle movement could create a dynamically shifting environment requiring angular acceleration of 120°/s2. Satellite communication on the move (SOTM) requires full hemispherical coverage. In addition, Low Earth Orbiting (LEO) satellites are not geosynchronous and therefore require continuous tracking.
Electronically steerable antennas (ESAs) can achieve a pointing accuracy of less than 0.5° but any individual planar ESA has only a limited steering range. Planar arrays are the least complex and most commonly used ESA; therefore, multiple planar, expensive ESAs are required to achieve full hemispherical coverage. Spherical ESA are capable of full hemispherical coverage but they are large, complex, expensive and aerodynamically unattractive for airborne applications.
Mechanically steerable antennas with two dimensions of movement can achieve full hemispherical coverage with a single antenna. However, the motion control system for military sitcom on the move (SOTM) is extremely complex and costly. It is very challenging to hold a lock on a satellite system while traversing over rough terrain in a ground vehicle when the SOTM antenna has a very narrow beam width, which can be a on the order of 1 degree for Q band systems. The inertial mass, moment arm and center of gravity of the antenna group (antenna positioner, RF front end, modem, etc.) of a typical SOTM antenna group makes motion control with high rates of acceleration with pointing accuracies within 0.5° very challenging. The required motion control systems are expensive, heavy and subject to mechanical failure. Furthermore, mechanically steerable systems are inherently slower than electronically steerable systems.
Consequently, it would be advantageous if a lightweight, cost-effective apparatus existed that is suitable for accurately positioning a satellite antenna in a dynamic environment.